1) If you break something because you don't know what you're doing when you take it apart, that isn't a "tech issue". That is a problem you created. Tech issues stem from bugs, manufacturing defects, or other errors that are not a product of misuse.
2) It's in quotation marks because a tear down to see the internals of the computer serves no purpose to the end user watching the video. It doesn't really "serve a purpose" to anyone except curious minds. It's not like anyone can watch the video and build an iMac from parts they bought at a hardware store, and given his results, they sure as shit aren't putting on back together. Not to mention Apple made it pretty clear that the internals are exceptionally delicate and "crammed in there", which is why it has absolutely zero upgradability (because of the way the cooling system works and everything else, having all that power in such a tiny case is difficult, so there wasn't "room" to offer expansion).
3) It's slimy because Linus absolutely knew all of these things going into his tear down. He knew that the machine was factory sealed, and crammed to the brim with hardware. He knew that it wasn't upgradeable. He knew that he would void the warranty. He almost certainly knew that you cannot buy OEM parts for an Apple product off the counter like you would any other components. These are not secrets or newly discovered bits of information. I find it EXTREMELY hard to believe that given his "profession", he was completely unaware of these conditions and the risks involved. He knew very well that he could end up breaking the machine, he knew he probably couldn't get his hands on replacement parts, and he knew it would be out of warranty. Hell he probably knew that he'd run into some trouble trying to get it fixed. Yet he puts on a show of complete shock, like all of these things were unexpected. It's a conflict of interest because he's exploiting his user base for profit by pretending he was wronged. He kicks off his video with an extremely vague description of the situation and then IMMEDIATELY gets into his sponsorship to make money. Can you not see how disingenuous this is?
I get it, fuck Apple, whatever, but that doesn't apply here. This is a jack ass who tore open an expensive piece of hardware, knowing full well what he was getting into, and then pretending that he was the victim of malpractice. He's exploited the tear down and the subsequent consequences of his action for profit, all while you feel some faux outrage, even though he genuinely does not give a shit about that iMac at all.
They bought it only to tear it open, which runs a significant risk to break it, considering the hardware in question. The iMac Pro is not an OEM Laptop or a desktop PC someone built using over the counter parts. It isn't the best PC you can buy, but it absolutely is a complicated piece of kit that requires expertise, thus him buying it and thinking he could repair it is questionable, and he likely knew going in (or he's just very stupid) that something would go wrong. They didn't buy it to use it for Video production, they bought it to open it up and marvel at the guts, which runs a great risk of destroying the hardware. Literally every tear down video out there (from professionals) acknowledges this.